The present invention relates to an improved Trip Circuit Supervision relay for Low and Medium Voltage applications. The Trip Circuit Supervision relay of the invention is conveniently used in trip circuits of Low or Medium Voltage apparatuses (e.g., circuit breakers, contactors, disconnectors). Low or Medium Voltage apparatuses including a trip circuit and a Trip Circuit Supervision relay as described herein are also part of the present invention. For the purposes of the present application the term medium voltage is referred to applications in the range of between 1 and 50 kV and low voltage is referred to applications in the range below 1 kV.
With reference to FIG. 1, a conventional trip circuit 10 in an apparatus, such as a Medium Voltage circuit breaker, controls the opening and closing driver 12, i.e. the mechanism/electronics driving the opening and closing operations, through, e.g. a switch 13.
In traditional mechanical circuit breaker, the driver 12 is a shunt release consisting in an electromagnet that releases a spring. As a result, the spring performs the required opening or closing operation. In modern circuit breakers and switches, the trip circuit 10 drives binary inputs of an electronic device 12. The electronic device 12, e.g. a power and control unit, processes the commands received from the trip circuit 10 and drives the actuators (not shown), such as motors, electromagnets, etc., to operate the circuit breakers and switches.
In all cases, in order to have highly reliable applications, it is important to check continuously the trip circuit 10 to make sure that it will work when required. To this purpose, Trip Circuit Supervision (TCS) relays 11 are normally used, said TCS relay being capable to detect the functionality of the trip circuit 10 and generate an alarm signal 15, by e.g., closing a contact 14.
Common Trip Circuit Supervision relay 11 are designed to check the low impedance of the trip circuit 10 and to detect when the trip circuit 10 turns into an open circuit. This occurs when the connection is broken or the wire of the electromagnet winding is burned by an overcurrent.
However, the open circuit is only one of the potential failure modes of the shunt release. Modern Low and Medium Voltage apparatuses, e.g. Medium Voltage circuit breakers, employ shunt releases with electronic drivers 12 that reduce significantly the probability of the open circuit failure. However, other failure modes, which cannot be detected by common Trip Circuit Supervision relays of the above type, are more likely.
Another type of Trip Circuit Supervision relay measures continuously the shunt releases winding electrical resistance. This Trip Circuit Supervision relay is able, in principle, to detect any failure in the winding. Unfortunately it can be used only for electromagnetic actuators, without electronic driver.
As a matter of fact, none of the existing Trip Circuit Supervision relays is able to detect failures, such as short circuit of the binary inputs (or shunt release) and any other type of failure in the electronic circuit of the binary input of the power and control unit, because a current may continue to flow in the trip circuit.